1. Field of the Invention
Certain embodiments of the present invention relate generally to composite materials and, in particular, relate to systems and methods for reinforcement of polymer matrices with low concentrations of uniformly dispersed nanomaterials.
2. Description of the Related Art
Composite materials have been developed to meet increasing demands for materials possessing a broad array of desirable properties. Composites are material systems which combine two or more distinct materials, each with its own distinctive, desirable properties, to create a new material with properties that may not be present, or to the same extent, in the components alone. Composite materials, broadly, possess at least two phases—a reinforcement and a matrix. The reinforcement is a material which is embedded within the matrix. In general, the reinforcing material and the matrix material may comprise any combination of metals, ceramics, or polymers.
In one example polymer matrix composites (PMCs) combine strong reinforcing fibers within a polymer matrix. Advantageously, PMCs possess relatively high strength, low weight, and corrosion resistance, which has spurred their development for applications in aerospace, sporting goods, automotive, and other industries where environmental and weight concerns play a key role in design considerations. Furthermore, these materials may be fabricated at relatively low costs, further increasing their desirability.
The use of polymers as matrix materials in composites demands excellent mechanical performance over a large range of temperatures. A limiting factor in the use of polymer matrices, however, is their relative brittleness and tendency to exhibit microcracking at low levels of strain. These microcracks may coalesce under load, forming macrocracks, and due to the relative brittleness of the polymer matrices, result in catastrophic failure with little warning. And while design strains can be kept to low levels to prevent microcracking and catastrophic failure, additional composite material is required to bear the applied load, increasing the total weight of the composite structures.
To mitigate the brittleness and microcracking of polymer matrices, researchers have experimented with the addition of nano-scale materials to polymer matrices in order to improve their strain to failure and fracture toughness. Nano-scale materials possess great promise as composite reinforcements. In general, the greater the surface to volume ratio of a reinforcement, the greater the effectiveness of a material as a reinforcement, and nano-scale materials have a high surface to volume ratio owing to their small size.
Agglomeration, however, has been a significant obstacle to the use of nano-scale materials as reinforcements. Small particles, those having a diameter less than approximately 1 μm, have a strong tendency to agglomerate, or group together, under the influence of Van der Waals forces. In the case of submicron particles, these forces are stronger than gravitational forces and gives rise to spontaneous agglomeration. Agglomerated particles contain small voids which are difficult for the reinforcing matrix to enter by capillary action during processing of the composite. Thus, a reinforced composite formed with agglomerates possesses voids which can act as flaws that, instead of benefiting the composite, are detrimental to its mechanical properties. In particular, a number of studies have observed that the addition of nano-scale materials may improve some mechanical properties, such as fracture toughness or stiffness, while other mechanical properties, such as strength, are detrimentally affected to the point where properties of the composite are less than that of the matrix alone.
Thus, there is need for an improved systems and methods of manufacturing composites reinforced with nano-scale materials and, in particular, polymer matrix composites which have improved fracture properties without incurring substantially detrimental impact upon other mechanical properties.